U.S. patent number 5,852,609 [Application Number 08/763,414] was granted by the patent office on 1998-12-22 for method and apparatus for interfacing a media independent interface with dvb-compliant modulators.
This patent grant is currently assigned to Intel Corporation. Invention is credited to Lewis E. Adams, III, Christopher L. Spearman.
United States Patent |
5,852,609 |
Adams, III , et al. |
December 22, 1998 |
**Please see images for:
( Certificate of Correction ) ** |
Method and apparatus for interfacing a media independent interface
with DVB-compliant modulators
Abstract
A method for interfacing a media independent interface with a
DVB compliant modulator includes the step of receiving nibbles of
data from a media independent interface in accordance with a
transmit clock signal and a holdoff signal during assertion of a
transmit enable signal, wherein the nibbles of data are a portion
of a variable sized packet. The nibbles of data are stored into a
first buffer. The transmit clock signal is disabled. The nibbles of
data are shifted out of the first buffer in accordance with a
serial clock signal to provide a first bitstream. The first
bitstream is framed into a predetermined packet size. The holdoff
signal is asserted to halt the first bitstream. A synchronization
indicator is serially inserted into the first bitstream in
accordance with the serial clock signal to form a second bitstream.
The second bitstream is parallelized to form parallelized data. The
parallelized data and a synchronization signal corresponding to the
synchronization indicator are synchronously provided in accordance
with a parallel clock signal.
Inventors: |
Adams, III; Lewis E. (Phoenix,
AZ), Spearman; Christopher L. (Tempe, AZ) |
Assignee: |
Intel Corporation (Santa Clara,
CA)
|
Family
ID: |
25067786 |
Appl.
No.: |
08/763,414 |
Filed: |
December 11, 1996 |
Current U.S.
Class: |
370/465; 370/366;
375/E7.021; 375/E7.002; 375/E7.025 |
Current CPC
Class: |
H04L
47/22 (20130101); H04L 47/10 (20130101); H04Q
11/0435 (20130101); H04Q 2213/13209 (20130101); H04Q
2213/13213 (20130101); H04Q 2213/13204 (20130101); H04Q
2213/13199 (20130101); H04Q 2213/13332 (20130101); H04Q
2213/1336 (20130101); H04Q 2213/13174 (20130101); H04Q
2213/13337 (20130101) |
Current International
Class: |
H04N
7/24 (20060101); H04L 12/56 (20060101); H04Q
11/04 (20060101); H04J 003/16 () |
Field of
Search: |
;370/389,395,366,412,503,427,507,512,516,518,520,445
;375/351,352 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Media Access Control (MAC) Parameters, Physical Layer, Medium
Attachment Units, and Repeater for 100 Mb/s Operation, Type
100BASE-T (Clauses 21-30), IEEE Standards for Local and
Metropolitan Area Networks: Supplement to Carrier Sense Multiple
Access with Collision Detection (CSMA/CD) Access Method and
Physical Layer Specifications, IEEE Std 802.3u-1995 (Supplement to
ISO/IEC 8802-3: 1993 [ANSI/IEEE Std 802.3, 1993 Edition]), The
Institute of Electrical & Electronics Engineers, Inc., 1995
..
|
Primary Examiner: Ton; Dang
Assistant Examiner: Sam; Phirin
Attorney, Agent or Firm: Blakely, Sokoloff, Taylor &
Zafman
Claims
What is claimed is:
1. A method for interfacing a media independent interface with a
Digital Video Broadcast (DVB) compliant modulator, comprising the
steps of:
a) receiving nibbles of data from the media independent interface
in accordance with a transmit clock signal and a holdoff signal
during assertion of a transmit enable signal, wherein the nibbles
of data are a portion of a variable sized packet;
b) storing the nibbles of data into a first buffer;
c) disabling the transmit clock signal;
d) shifting the nibbles of data out of the first buffer in
accordance with a serial clock signal to provide a first
bitstream;
e) framing the first bitstream into a predetermined packet
size;
f) asserting the holdoff signal to halt the first bitstream;
g) serially inserting a synchronization indicator into the first
bitstream in accordance with the serial clock signal to form a
second bitstream;
h) parallelizing the second bitstream to provide parallelized
data;
i) synchronously providing the parallelized data and a
synchronization signal corresponding to the synchronization
indicator in accordance with a parallel clock signal.
2. The method of claim 1 wherein a nominal frequency of the
transmit clock is approximately 25 MHz.
3. The method of claim 1 wherein a nominal frequency of the serial
clock is approximately 38.1 MHz.
4. The method of claim 1 wherein a nominal frequency of the
parallel clock is approximately one-eighth a nominal frequency of
the serial clock.
5. The method of claim 1 further comprising the steps of:
j) continuously inserting an idle byte into the first serial
bitstream in accordance with the serial clock signal while the
transmit enable signal is de-asserted.
6. The method of claim 5 wherein a value of the idle byte is
distinct from a preamble of the variable sized packet.
7. The method of claim 1 further comprising the steps of:
j) inserting an end of packet indicator into the first serial
bitstream in accordance with the serial clock signal when the
transmit enable signal transitions from an asserted state to a
de-asserted state.
8. The method of claim 7 wherein the end of packet indicator is a
sequence beginning with a "0" followed by fifteen "1"s.
9. The method of claim 1 further comprising the step of:
j) inserting a "0" into the first serial bitstream, if the variable
sized packet includes a sequence of "0" followed by sixteen "1"s,
wherein the "0" is inserted into the first serial bitstream after
the fifteenth "1".
Description
FIELD OF THE INVENTION
This invention relates to the field of communications. In
particular, this invention is drawn to providing an interface
between an IEEE 802.3 u media independent interface and a
DVB-PI-227 compliant modulator.
BACKGROUND OF THE INVENTION
Remote access to a server on a computer network is often gained
through the use of a telephone modem. For example, individuals
communicating on the Internet typically access an Internet Service
Provider using a dial-in modem and a telephone line in order to
connect with a server.
One disadvantage of a standard telephone modem is that data
communication rates are presently practically limited to
approximately 28.8 kilobaud/second. At this rate, downloading a
large file (e.g., several megabytes) may take a considerable amount
of time.
Some servers accessed by the remote user may be using data
communication equipment based on Ethernet or Fast Ethernet
standards which permit data communication rates up to 10 Mb/s and
100 Mb/s, respectively.
T1 and Integrated Services Digital Network (ISDN) telephone lines
are available for greater communications speed than possible with a
standard telephone line. Unfortunately, none of the standard, T1,
nor ISDN telephone lines permit communication at 10 Mb/s or 100
Mb/s rates. The maximum data communications rate for T1 or ISDN
telephone lines is considerably less than 10 Mb/s (i.e., at least
one order of magnitude less).
In addition, T1 and ISDN telephone lines are substantially more
expensive to install and use than standard telephone lines.
Furthermore, the modems required for T1 and ISDN data communication
rates are considerably more expensive than standard telephone
modems.
An alternative to a dial-up connection is to use a direct
connection to each server that the remote user wishes to
communicate with. This alternative, however, tends to be
prohibitively expensive and impractical for a even a small number
of clients.
Thus the communications link between the remote user and the server
tends to be one of the primary bottlenecks in achieving greater
data communication rates between remote users and servers on
computer networks.
SUMMARY OF THE INVENTION
In view of limitations of known systems and methods, a method for
interfacing a media independent interface with a DVB compliant
modulator is provided. The method includes the step of receiving
nibbles of data from a media independent interface in accordance
with a transmit clock signal and a holdoff signal during assertion
of a transmit enable signal, wherein the nibbles of data are a
portion of a variable sized packet. The nibbles of data are stored
into a first buffer. The transmit clock signal is disabled. The
nibbles of data are shifted out of the first buffer in accordance
with a serial clock signal to provide a first bitstream. The first
bitstream is framed into a predetermined packet size. The holdoff
signal is asserted to halt the first bitstream. A synchronization
indicator is serially inserted into the first bitstream in
accordance with the serial clock signal to form a second bitstream.
The second bitstream is parallelized to form parallelized data. The
parallelized data and a synchronization signal corresponding to the
synchronization indicator are synchronously provided in accordance
with a parallel clock signal.
Other features and advantages of the present invention will be
apparent from the accompanying drawings and from the detailed
description that follows below.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example and not
limitation in the figures of the accompanying drawings, in which
like references indicate similar elements and in which:
FIG. 1 illustrates the correspondence between the ISO Open Systems
Interconnect Reference Model, the IEEE Std. 802.3 u-1995 model, and
the Media Independent Interface-Digital Video Broadcoast
(MII-DVB)interface.
FIG. 2 illustrates communications between an IEEE 802.3 u-1995
compliant media independent interface, the MII-DVB interface, and a
DVB modulator.
FIG. 3 illustrates components of the MII-DVB interface.
DETAILED DESCRIPTION
The Institute of Electrical and Electronics Engineers has set forth
a number of standards for local and metropolitan area networks. In
particular, CSMA/CD Access Method and Physical Layer Specifications
(IEEE 802.3-1993) is a standard governing standard Ethernet
networks. In accordance with IEEE 802.3-1993, standard Ethernet is
capable of approximately 10 Mb/s maximum throughput.
Another Ethernet standard entitled "Media Access Control (MAC)
Parameters, Physical Layer, Medium Attachment Units, and Repeater
for 100 Mb/s Operation, Type 100BASE-T" (IEEE Standard 802.3u-1995)
has been designed to provide for 100 Mb/s using the same Carrier
Sense Multiple Access/Carrier Detect (CSMA/CD) access method as
standard Ethernet. Due to the ten-fold increase in data rates, this
standard is also referred to as Fast Ethernet.
Fast Ethernet provides for a Media Independent Interface. The Media
Independent Interface allows coupling of Data Communication
Equipment having different OSI model physical layer implementations
(e.g., 100BASE-T, 100BASE-T4, 100BASE-TX, 100BASE-X, and
100BASE-FX).
FIG. 1 illustrates the application of IEEE Std. 803.2u-1995 (Fast
Ethernet) to the 7-layer OSI Reference Model 110. In particular,
the IEEE Std. 803.2u-1995 provides for a Media Independent
Interface 130 for coupling to various embodiments of the Physical
Layer Entity (PHY). PHY is coupled to a pre-determined medium 140
using a Medium Dependent Interface (MDI). The standard only
supports specified mediums (140) include 100Base-T, 100Base-TX,
100Base-FX, and 100Base-X.
One medium which may provide greater communication rates than
dial-in connections is the network of community antenna television
(CATV) coaxial cable available for distributing cable television
programs to viewers. The network of CATV associated with a given
distribution center or "headend" is referred to as a cable
plant.
The headend was previously used to transmit primarily analog video
data. Standards have been promulgated, however, for transmission of
digital data using available analog broadcast equipment.
In particular, the Digital Video Broadcast (DVB) committee of the
European-based Digital Audio Video Industry Consortium (DAVIC) has
developed some of these standards. One standard for encoding
digital data for transmission using standard television broadcast
equipment is referred to as DVB-PI-227. For example, "DVB-PI227
Interfaces for CATV/SMATV Headends and Similar Professional
Equipment (Draft TM1449 Rev. 2, Jun. 6, 1996)" describes physical
interfaces for the interconnection of digital signal processing
devices for professional CATV/SMATV headend equipment or for
similar systems, such as in uplink stations. "Headend" includes
equipment connected between receiving antennas or other signal
sources and the remainder of the cable plant. The headend may
include, for example, antenna amplifiers, frequency converters,
combiners, separators, modulators, and generators.
Unfortunately DVB-PI-227 uses media, signals, and protocols,
however, which are incompatible with those of the Fast Ethernet,
IEEE Std. 802.3u-1995. Thus the MII interface and DVB-PI-227
compliant equipment are not immediately compatible.
The media independent interface (MII) is a readily available
interface found in Fast Ethernet data communication equipment such
as a 7200 series router manufactured by Cisco Systems, Inc. of San
Jose, Calif. The Mul is implemented as an MII port on the data
communication equipment. The operation and control of the MII port
is governed by IEEE Std. 802.3u-1995 entitled "Media Access Control
(MAC) Parameters, Physical Layer, Medium Attachment Units, and
Repeater for 100 Mb/s Operation, Type 100BASE-T" which is
explicitly incorporated herein by reference (hereinafter "IEEE
802.3u").
Commercially available DVB PI-227 compliant modulators (hereinafter
"DVB modulators") use varying schemes for modulating the digital
data depending upon the method of broadcast. For example,
Quadrature Phase Shift Keying (QPSK) modulation is typically used
with headend equipment for satellite communications. Quadrature
Amplitude Modulation (QAM) is typically used with headend equipment
for television and CATV applications. Each of the DVB modulation
schemes, however uses a common data input standard governed by the
DVB-PI-227 specification. The data input standard is described, for
example, in DVBPI-227 Interfaces for CATV/SMATV Headends and
Similar Professional Equipment (Draft TM1449 Rev. 2, Jun. 6, 1996)
which is explicitly incorporated herein by reference (hereinafter
"DVB-PI-227").
One example of a DVB modulator for modulating digital signals for
communication on CATV and SMATV headend equipment include the
QAMLink BCM93120 DVB Development System, manufactured by Broadcom
Corporation of Irvine, Calif. Another example of a DVB modulator is
the QAM DVB Modulator manufactured by Tonna Electronique of France.
FIG. 1 illustrates the correspondence between the 7-layer ISO Open
Systems Interconnect Reference Model (140), the IEEE Std.
802.3u-1995 model (130), and the MII-DBV interface (100). MII-DVB
interface 100 replaces the PHY sublayers. In particular, MII-DVB
interface permits coupling MII layer 110 to a DVB modulator 120 for
subsequent distribution of the signal to a headend for CATV/SMATV
broadcast. Thus medium 160 can be any medium coupled to a
CATV/SMATV headend including coaxial cable or space (for satellite
transmissions).
FIG. 2 illustrates an MII-DVB interface 200 for communicating data
between an IEEE 802.3u-1995 compliant media independent interface
210 and an industry standard DVB modulator 220. A description of
the signals as they correspond to signals defined by their
respective governing standards is described below.
MII.sub.-- TDATA 262 corresponds to the IEEE 802.3u Transmit Data
(TXD) signal. MII.sub.-- TDATA is a bundle of 4 data signals
(corresponding to a four bit bus) provided by the MII. Thus data is
transferred as serial nibbles of data.
MII.sub.-- TXEN 264 corresponds to the IEEE 802.3u Transmit Enable
(TX.sub.-- EN) signal. MII.sub.-- TXEN 214 indicates whether
nibbles of data are presented for transmission from the MII.
MII.sub.-- CLSN 266 is provided by the MII.sub.-- DVB interface
200. MII.sub.-- CLSN corresponds to the IEEE 802.3u Collision
Detected (COL) signal. MII.sub.-- CLSN 216 is asserted by the
MII-DVB interface upon detection of a collision and remains
asserted while the collision condition persists. In one embodiment,
MII.sub.-- CLSN 216 is not implemented. In an alternative
embodiment, MII.sub.-- CLSN 266 is provided to permit a request to
resend the packet.
MII.sub.-- CRS 268 is provided by the MII.sub.-- DVB interface 200.
MII.sub.-- CRS corresponds to the IEEE 802.3u Carrier Status (CRS)
signal.
MII.sub.-- TCLK 270 corresponds to the IEEE 802.3u Transmit Clock
(TX.sub.-- CLK) signal. The Transmit Clock (TX.sub.-- CLK) signal
is defined as a continuous clock that provides the timing reference
for the transfer of the TX.sub.-- EN, TXD, and TX.sub.-- ER
signals. The TX.sub.-- CLK frequency is defined as approximately
25% of the nominal transmit data rate.
MII.sub.-- MDIO 242 and MII.sub.-- MDC 244 correspond to the IEEE
802.3u Management Data Input/Output (MDIO) and Management Data
Clock (MDC) signals, respectively. MII.sub.-- MDC serves as the
timing reference for transfer of information on the MII.sub.-- MDIO
signal line. MII.sub.-- MDIO is a bidirectional signal used to
transfer control information and status between the MII and the
MII-DVB interface. MDC is provided by the MII.
The data frame structure transmitted through the MII has a frame
format including an inter-frame, a preamble, a start of frame
delimiter (SFD), transmitted data, and an end of frame delimiter
(EFD).
The inter-frame corresponds to an absence of data activity such as
the period between transmission or receipt of subsequent Ethernet
packets. The inter-frame is indicated by the de-assertion of the
MII.sub.-- TXEN. The preamble begins a frame transmission. IEEE
802.3u specifies sending 8 bits of alternating "1" and "0" bit
values seven times in order to indicate the beginning of a frame
transmission (i.e., in order of transmission the preamble is
10101010 transmitted seven times). SFD indicates the start of a
frame and follows the preamble. The bit value of the SFD in the bit
order of transmission is specified as 10101011. The data
transmitted in a well formed frame consists of n octets of data
transmitted as 2n nibbles. MII.sub.-- TXEN is asserted to indicate
data is ready to be transmitted during transmission of the
preamble, the SFD, and the data. De-assertion of the MII.sub.--
TXEN signal constitutes an end of frame delimiter and therefore
signals the end of a packet for Ethernet packets.
DVB-PI-227 requires that data be in an MPEG-2 transport stream
packet. The packets are 188 or 204 byte packets. DVB-PI-227
provides for a parallel interface for communicating the packets
using a clock signal, a data signal, a valid data signal, and a
synchronization signal as described below.
PDATA 282 corresponds to DVB-PI-227 8 bit data bus. PDATA is used
to communicate the data to be transmitted from the MII-DVB
interface 200 to the DVB compliant modulator 220.
PSYNC 286 corresponds to the DVB-PI-227 PSYNC signal. PSYNC is a
synchronization signal used to indicate the beginning of a DVB
frame from MII-DVB interface 200. A DVB frame may optionally be a
188 byte frame or a 204 byte frame. One byte of the 188 byte or 204
byte frame is used for synchronization leaving either 187 bytes or
203 bytes for data, respectively. For 204 byte frames, up to 16
bytes may be padding bytes for ease of compatibility with the 188
byte frame format.
DVAL 284 corresponds to the DVB-PI-227 DVALID signal. DVAL 284 is
used to indicate when PDATA 282 includes padding bytes. PCLK 288
corresponds to the DVB-PI-227 clock signal. PCLK 288 is used for
synchronous transmission of the DVAL, PSYNC, and PDATA signals to
the DVB modulator 220.
FIG. 3 illustrates functional blocks of the MII-DVB interface 300
(i.e., MII-DVB interface 210 in FIG. 2.) MII-DVB interface 300
includes 4 functional blocks: serial interface (SIF) 310, MPEG-2
synchronization and packet id insertion 320, DVB parallel
conversion 330, and MII management interface 340.
MII management interface 340 is required for compliance with IEEE
802.3u. At a minimum, MII Management Interface 340 provides a
control register and a status register which can be accessed by the
MII using the MDIO 242 bidirectional signal in accordance with the
MDC 244 signal. Management Interface 340 uses a frame format and a
protocol specification for exchanging management frames as set
forth in IEEE Std 802.3u-1995 at .sctn. 22.2.4.
Serial interface 310 serializes the data received from an MII port.
SIF 310 performs a serial nibble to serial bit conversion, data
rate throttling of the MII, zero bit insertion, end of packet (EOP)
insertion, and idle data insertion.
Data rate throttling is necessary because the DVB modulator cannot
transmit data at 100 Mb/s even though the MII may provide the data
at 100 Mb/s. Data rate throttling is accomplished by controlling
MII.sub.-- TCLK.
As stated above, MII.sub.-- TXEN 264 is asserted when valid data is
available on the MII.sub.-- TDATA bus 262. When MII.sub.-- TXEN is
enabled, MII.sub.-- TDATA is received serially as nibbles at a rate
determined by MII.sub.-- TCLK 270. During the time MII.sub.-- TXEN
is asserted, SIF 310 first generates a single clock pulse on
MII.sub.-- TCLK. This pulse serves to load a buffer within SIF 310
with the contents of MII.sub.-- TDATA. In one embodiment, the
buffer is a first in first out (FIFO) buffer.
The contents of the buffer are shifted out through SDATA 392 at a
rate determined by the serial clock signal SCLK 390. In one
embodiment, when the last bit is shifted, SIF 310 generates another
single clock pulse on MII.sub.-- TCLK 270 to load another nibble of
data into the buffer. In another embodiment, MH.sub.-- TCLK clock
pulses are provided until the buffer is full before the buffer is
serially shifted out through SDATA 392.
The data received from the MII port is part of a variable length
packet. Once the entire packet has been transmitted by the MII
port, the MII.sub.-- TXEN signal is de-asserted. Upon de-assertion
of the MII.sub.-- TXEN signal, the MII-DVB interface 310 provides a
continuous MII.sub.-- TCLK clock signal to the MII port. Thus the
data rate is throttled when MII.sub.-- TXEN is asserted by
controlling MII.sub.-- TCLK to prevent receiving subsequent nibbles
of data until SDATA has been serially shifted out at a rate
determined by SCLK.
The nominal MII.sub.-- TCLK frequency should not exceed 25% of the
nominal transmit data rate of the data communications equipment. In
one embodiment, the MII.sub.-- TCLK nominal frequency is 25 MHz
(i.e., for 100 MHz data communications equipment). In another
embodiment, the MII.sub.-- TCLK nominal frequency is 2.5 MHz (i.e.,
for 10 Mb/s data communications equipment).
SIF 310 generates the MII.sub.-- CRS 266 signal from the received
MII.sub.-- TXEN 264 signal. This can be accomplished, for example,
by providing the MII.sub.-- TXEN signal for return transmission as
the MII.sub.-- CRS signal.
MII.sub.-- TXEN 264 transitions from asserted to de-asserted to
indicate the end of a packet of data. SIF 310 generates an end of
packet (EOP) indicator for the serial data stream in order that the
end of packet can be detected within the serial data stream without
the use of additional control signals. In one embodiment, the EOP
indicator is a sequence of a "0" followed by sixteen "1" s output
serially through SDATA when MII.sub.-- TXEN transitions from an
asserted to a de-asserted state.
In order to ensure that EOP is distinct from the actual packet
data, a "0" bit is inserted after any sequence of 15 "1" s. This
zero bit insertion ensures that EOP is unique from the data being
transmitted. The zero bit insertion can be accounted for by data
communications equipment and data terminal equipment at the
receiving end by removing any "0" bit immediately following a
series of 15 ones. If a "0" followed by 15 "1" s is received, then
the receiving end should assume an EOP has been received.
The length of the IEEE 802.3u inter-frame is variable. Once an EOP
has been received, there is no expectation as to when the next
packet will be transmitted. Broadcast carriers, however, should be
continuously modulated. The DVB modulator therefore should
continuously receive transmission data in order to ensure a
continuously modulated broadcast carrier. This is accomplished by
the insertion of idle bytes into the serial data stream.
Once the EOP has been inserted into the serial data stream provided
by SDATA, an idle data pattern is inserted into the SDATA
bitstream. This can be accomplished by continuously placing idle
data bytes in the buffer and serially shifting them out through
SDATA 392 until MII.sub.-- TXEN 264 is asserted again.
The value of the idle data byte is selected to ensure that the
received data is not interpreted as a start of packet. In order to
ensure that the received data is not interpreted as a start of
packet, the value of the idle byte is selected to be unique from
the IEEE 802.3u preamble definition (i.e., "10101010"). In one
embodiment, the idle byte has the value "00110011," however any
value unique from the sequence "10101010" is acceptable.
The bitstream generated by the SIP 310 block is provided to block
320 for MPEG-2 synchronization. Block 320 also permits optional
insertion of program identification description (PID) for
transmission. Block 320 counts the number of bytes received from
the SDATA bitstream while providing the SDATA bitstream to block
330 through SDATA.sub.-- M 396. SDATA.sub.-- M is also clocked by
SCLK 390.
Once SDATA has provided 187 bytes, block 320 asserts the HOLDOFF
signal. HOLDOFF disables the SIF 310 from clocking the SDATA
bitstream when asserted. While HOLDOFF is asserted, block 320
inserts a synchronization byte (e.g., 0.times.47) into the SDATA
bitstream so that the SDATA.sub.-- M bitstream comprises the SDATA
bitstream plus a synchronization byte. The PSYNC.sub.-- M 398
signal is asserted while the synchronization byte is being serially
shifted into the SDATA.sub.-- M bitstream. MPEG-2 data frames
permit up to 204 bytes of data, thus 16 bytes are available and can
consist of padding or other data. These 16 bytes can be used to
insert PID information if desired. PID information can be used to
indicate the content of the data or the source of the data. After
insertion of the synchronization byte and optional PID information
into the SDATA.sub.-- M bitstream, the byte count is initialized to
zero and HOLDOFF is de-asserted.
Block 330 performs the conversion of the serial bitstream from
SDATA.sub.-- M into a parallel data format for the DVB modulator.
Serial data from SDATA.sub.-- M 396 is clocked into a buffer using
the SCLK 390 signal. The frequency of the SCLK signal is divided by
8 to provide the PCLK 288 signal. DVALID, PSYNC, and PDATA are
synchronous to PCLK.
When PCLK 288 is asserted, the contents of the buffer are latched
to provide the PDATA 282 signal. The status of PSYNC.sub.-- M 398
is latched to provide the PSYNC 284 signal. Thus PSYNC.sub.-- M is
effectively delayed by 8 SCLK cycles to provide PSYNC.
DVB-PI-227 specifies Low Voltage Differential Signaling (LVDS) for
the synchronous parallel interface. Thus, for example, if
complementary metal oxide semiconductor (CMOS) or
transistor-transistor logic (TTL) devices are used then LVDS
drivers may be required to provide CMOS-to-LVDS or TTL-to.sub.--
LVDS signal conversion. In one embodiment, block 330 includes
drivers to provide LVDS levels for the synchronous parallel
interface. SCLK is selected to have a frequency compatible with the
DVB modulation equipment. In one embodiment, SCLK is approximately
38.1 MHz.
The MII-DVB interface discussed above is particularly suitable for
asymmetrical communications between a remote user and a server. For
example, users who browse the World Wide Web on the Internet tend
to retrieve (i.e., download) considerably more information than
they upload. This results in a larger bandwidth requirement for
downstream communications (i.e., to the remote user) than upstream
communications (i.e., to the server).
Given that the DVB-PI-227 standard is directed to SMATV and CATV
applications, an MII-DVB interface provide Fast Ethernet packets to
a headend which can provide the packets to a remote user via
multiple transmission mediums including satellite or CATV
distribution networks.
Standard telephone modems may serve to adequately support the
upstream data rates. The data is retrieved downstream by tuning a
DVB demodulator to a particular channel. Thus a microprocessor
based personal computer can achieve significantly greater
bidirectional communication rates using a standard telephone modem
in conjunction with pre-existing CATV coaxial connections.
Furthermore, the DVB modulated packet data may be located on a CATV
channel such that reception of other CATV channels is not
impaired.
In the preceding detailed description, the invention is described
with reference to specific exemplary embodiments thereof. Various
modifications and changes may be made thereto without departing
from the broader spirit and scope of the invention as set forth in
the claims. The specification and drawings are, accordingly, to be
regarded in an illustrative rather than a restrictive sense.
* * * * *